The long-term objectives of this proposed project are to develop a "Test Kit" for quantitative assessment of steatorrhea in infants without the need for control of dietary fat intake and quantitative collections of stools for several days as is the case with the current "Gold Standard," viz, the 72-hour fecal fat method. Our proposed "Test Kit" is based on administering a feeding of infant formula containing a suitably labeled 13C-triglyceride (TG), a trace amount of the nonabsorbable marker dysprosium chloride (DyC1-3) and the visual marker Brilliant Blue followed by laboratory analysis of Dy and 13C-Excess in one or more sample(s) of stool containing the visual marker. The research conducted during Phase-I of this grant has led to the selection of 1,3-(13C-2) dipalmitoyl, 2-lauryl glycerol (P*LP*) as the most suitable TG* for applications in infants. During Phase II of the project, we propose to conduct clinical protocols with cystic fibrosis and healthy infants in order to: (1) define the parameters of the expected linear correlation between fecal excretion of P*LP* and fecal fat, (2) demonstrate the significance of this novel method in medical management of infants with steatorrhea, and (3) obtain research data necessary for the manufacture of a safe and noninvasive "Test Kit" for accurate assessment of steatorrhea in infants. The "Test Kit" has widespread applications in clinical management of infants with a wide range of disorders leading to steatorrhea.